1. Field of the Invention
Fiber optic probes, and particularly fiber optic catheters with particular reference to catheters intended for insertion into the cardiovascular system.
2. Description of the Prior Art
Various fiber optic probes require calibration if their intended use includes some type of measuring function. In-vivo fiber optic catheters which are sterilized before use require calibration in conjunction with their associated electro-optical equipment so that absolute values of oxygen saturation or dye concentration and/or accurate measurements of variations thereof with time are made possible in the performance of blood oxygen saturation determinations or dye dilution measurements with these catheters.
Previously, such catheter calibration has required that the distal end of the catheter be placed in a sterile suspension medium such as milk-of-magnesia which will give a fixed ratio of reflections or wavelengths of light such as 805 mu and 660 mu or others which may be used for blood oxygen saturation or dye dilution testing. This method of calibrating in-vivo catheters, however, is potentially dangerous to patients since portions of the suspension medium clinging to the catheter may become introduced into the patients blood stream. These inclusions in not being isotonic with blood and embolic, are potentially dangerous to the patient and, least wise, may adversely affect the accuracy of oxygen saturation determinations and/or other measurements taken with the in-vivo catheter and its associated equipment.
More recently, a smoothly surfaced ball was fixedly mounted in spaced relation with the end faces of the optical fibers at the distal end of the catheter for providing fixed reflections of light directed thereon from the catheter when in air or placed in clear sterile solution for calibration prior to use, as described in U.S. Pat. No. 3,807,390 issued Apr. 30, 1974 to Ostrowski and Polanyi for FIBER OPTIC CATHETER and assigned to the assignee of the present invention. The ball was supported in position by a cage affixed to the distal end of the catheter and was carried with the catheter into the patient's blood stream. However, the manufacture of the small ball and its cage, and their installation on the distal end of the catheter is complicated by the relatively small dimensions involved. For instance, some catheters may have a diameter of as little as 1 millimeter or less. Additionally, the ball and cage structure tend to make the distal end of the catheter inflexible, which may hinder the smooth passage of the catheter through small radius bends in the blood stream.
This invention makes it possible to calibrate fiber optic probes, and particularly in-vivo catheters, without the subsequent danger of introducing extraneous matter into the blood stream. Further, the present invention provides improved means for the calibration of fiber optic probes which means is readily adaptable to probes or catheters of even very small diameter and which is of relatively low cost. Still further, the present invention provides improved means for the calibration of in-vivo fiber optic catheters which means permit the distal end of the catheter to remain relatively flexible.